1. Field of the Invention
The present invention relates to a process for the production of polyurethanes, in particular polyurethane foams, in which hydroxy functional poly(dialkyl-aminoalkyl)-ethers are used as catalysts.
2. Description of the Prior Art
Polyurethanes having the most varied physical properties have for some time now been commercially produced according to the known isocyanate-poly-addition process from compounds having several active hydrogen atoms, in particular from compounds containing hydroxyl, amine and/or carboxyl groups, and from polyisocyanates, optionally by simultaneously using water and/or organic blowing agents, catalysts, emulsifiers and other additives (Angewandte Chemie, 59 (1948) P. 257).
It is possible by an appropriate choice of components to produce homogeneous or cellular products and flexible, elastic foams as well as rigid foams or any variants lying between these extremes.
Polyurethane foams are preferably produced by mixing liquid components, the starting substances which are to be reacted with each other being either simultaneously mixed together or a prepolymer having NCO-groups initially being produced with polyols which is then foamed.
In the production of polyurethane foam, tertiary amines have proved particularly successful as catalysts, in particular because they are capable of accelerating not only the reaction of hydroxyl and/or carboxyl groups and NCO-groups, but also the reaction between water and the isocyanate groups. The reactions which are simultaneously taking place in the one-stage ("one shot") process are coordinated with each other.
Moreover, during the foaming process, additional cross-linking reactions take place with the formation of allophanate, biuret and cyanurate structures. On account of the complexity of the reactions, the synchronous course must be guaranteed by a choice of a suitable catalyst.
Conventionally, tertiary aliphatic amines having a high vapor pressure, such as triethylamine, are used. These amines produce a balanced course of the competing reactions in the core of the foamed parts and in the peripheral region. After foaming, said amines diffuse out of the foams. Thus, the danger of amine-catalyzed decomposition reactions is reduced. Tertiary amines which have a low vapor pressure have, nevertheless, a strong, very unpleasant smell, and thus when they are used it either causes considerable discomfort to the work force in the factories or else extensive ventilation is required.
Therefore, numerous attempts have been made to use amine catalysts which have a relatively low vapor pressure and less of a smell and/or chemically incorporable amine catalysts which simultaneously react in the production of polyurethane.
When incorporable amine catalysts are used, the problem generally arises, that, on the one hand, the basicity and mobility of the catalyst was greatly reduced by incorporating it too rapidly into the polyurethane and, on the other hand, the stability of the completed foam was impaired (hydrolytic and thermal decomposition).
Surprisingly, it has now been found, that certain hydroxy-functional poly(dialkylaminoalkyl) ethers manifest a high activity throughout the course of the polyurethane formation, have a low vapor pressure and thus minimal smell, are chemically bound during the reaction and do not impair the stability of a completed polyurethane part.